The present invention relates to a rotary cam moving apparatus for a negative-angle forming die for forming a sheet metal. Herein, the negative-angle forming die is used for a formation made at a location more inward of a lower die half than a straight downward stroke line of an upper die half.
The negatively angled forming of a work provided as a sheet metal into a shape having a portion more inward of the lower die half than the straight downward stroke line of the upper die half is generally performed by using a slide cam.
According to a prior-art intrusion forming process of the sheet metal work, the work is placed on the lower die half and the upper die half is lowered vertically. At this time a drive cam of the upper die half drives a driven cam of the lower die half, forming the work from a side. After the formation is completed and the upper die half is lifted, then the driving cam is retracted by a spring.
In the above arrangement, the driven cam slid onto the work from the side has a forming portion which is formed as a single piece in the same shape as the work as after the formation. The lower die half however, must allow the work to be taken out from the lower die half after the formation, and for this reason, a portion of the lower die half providing the intrusion formation must be made separable for retraction, or a rear portion thereof must be cut off so that the work can be moved forward and taken out. This does not pose a serious problem if the extent of the intrusion is small. However, the problem becomes serious if the extent of the intrusion is large, or if the work is to be formed into a long frame having a groove-like section such as in a formation of an automobile front pillar-outer from a sheet metal. Specifically, since the groove width of the work is so narrow, that if the portion of the lower die half corresponding to the groove is divided or cut off, it becomes impossible for the forming portion of the driven cam to form clearly. In addition, strength of the lower die decreases. Thus, it was impossible to perform a clear-shaped intrusion formation.
Further, a formed product sometimes has a twist or distortion, which must be corrected. However, for example, many automobile parts that provide the outer skin of the automobile, such as a side panel, fender, roof, bonnet, trunk lid, door panel, front pillar-outer and so on are formed to have a three-dimensional surface or line, and therefore it is practically impossible to make correction after the formation. In assembling the automobile sheet-metal parts, if there is a twist or distortion in the parts, it is difficult to fit the parts together. Without solving this problem, it was impossible to provide a high quality automobile sheet metal structure, and it was impossible to maintain a required level of product accuracy in the formed sheet metal products.
In order to solve the above-described problem, an arrangement was proposed, in which the straight downward stroke of the upper die half is converted to a rotary movement of a rotary cam to pivot to form the portion in the lower die half more inward than the straight downward stroke line of the upper die half. In this arrangement, after the forming operation, the rotary cam is pivoted back to a state where the completed work can be taken out of the lower die. This arrangement will be described in more detail.
Specifically, as shown in FIG. 9 to FIG. 12, this negative-angle forming die comprises a lower die half 102 including a supporting portion 101 on which a work W is placed and an upper die half 103 which is lowered straightly down onto the lower die half 102 to press thereby forming the work W. The lower die half 102 is rotatably provided with a rotary cam 106 supported in an upwardly opening axial groove 104. The groove 104 has a portion close to the supporting portion 101 formed with an intrusion forming portion 105 located more inward than a stroke line of the upper die half 103. The lower die half 102 rotatably supports a rotary cam 106. The upper die half 103 is provided with a slide cam 108 opposed to the rotary cam 106 and provided with an intrusion forming portion 107. The lower die half is further provided with an automatic retractor 109 which moves the rotary cam 106 back to the sate that allows the work W to be taken out of the lower die half 102 after the formation. The work W placed on the supporting portion 101 of the lower die half 102 is formed by the intrusion forming portion 105 of the rotary cam 106 and the intrusion forming portion 107 of the slide cam 108. The work W is formed by a rotary movement of the rotary cam 106 and a sliding movement of the slide cam 108. After the formation, the automatic retractor 109 pivots back the rotary cam 106, allowing the work W to be taken out of the lower die half 102.
Now, an operation of this negative-angle forming die will be described.
First, as shown in FIG. 7, the upper die half 103 is positioned at its upper dead center. At this stage, the work W is placed on the supporting portion 101 of the lower die half 102. The rotary cam 106 is held at its retracted position by the automatic retractor 109.
Next, the upper die half 103 begins to lower, and first, as shown in FIG. 8, a lower surface of the slide cam 108 makes contact with a pivoting plate 111 without causing the slide cam 108 to interfere with the intrusion forming portion 105 of the rotary cam 106, pivoting the rotary cam 106 counterclockwise as in FIG. 8, thereby placing the rotary cam 106 at a forming position. Then, a pad 110 presses the work W.
When the upper die half 103 continues to lower, the slide cam 108 which is under an urge outward of the die half begins a sliding movement as the sliding cam in a laterally rightward direction, against the urge from a coil spring 112. This is a state shown in FIG. 9, where the intrusion forming portion 105 of the pivoted rotary cam 106 and the intrusion forming portion 107 of the slide cam 108 perform formation of the work W.
After the intrusion formation, the upper die half 103 begins to rise. The slide cam 108, which is urged outwardly of the die half by the coil spring 112, moves in a laterally leftward direction as in FIG. 10, and keeps rising without interfering with the work W as after the intrusion formation.
On the other hand, the rotary cam 106 is released from the holding by the slide cam 108, and therefore is pivoted in a rightward direction as in FIG. 10 by the automatic retractor 109. Thus, when the work W is taken out of the lower die half after the intrusion formation, the work W can be removed without interference of the rightward portion with the intrusion forming portion 105 of the rotary cam 106.
As shown in FIG. 11, formation of a flange 211 in the work W is made in a direction not in parallel with but across an axis of pivoting L of the rotary cam 213. After this formation, intrusion formation is performed to form a recessed portion 212. With this arrangement, when the rotary cam 213 retracts, the rotary cam 213 pivots in a retracting direction A of the rotary cam 213, deforming the flange 211 of the work W.
In this work W, the flange 211 is formed and then the recessed portion 212 is formed. As has been described in the prior art, the formation of the recessed portion 212 is made by placing the work W on the lower die half (not illustrated in FIG. 9) and on the rotary cam 213 of the negative-angle forming die. As shown partially in FIG. 11, the flange 211 is supported along a wall surface 214 of the rotary cam 213. The wall surface 214 of the rotary cam 213 is formed along a flange-direction line. After the formation of the recessed portion 212 of the work W, in order to take the work W as after the intrusion formation, the rotary cam 213 pivots back in the retracting direction A, with the work W being left on the lower die half. Because the work W is still in the lower die half when the rotary cam 213 is pivoting back in the retracting direction A, the wall surface 214 of the rotary cam 213 interferes with the flange 211 of the work W, and deforms the flange 211. The interference of the wall surface 214 of the rotary cam 213 with the flange 211 of the work W will not occur if the flange-direction line of the flange 211 is on an orthogonal line vertical to the axis of pivoting L of the rotary cam 213. In the other conditions however, the wall surface 214 will interfere with the flange 211, and deform the flange 211. In FIG. 11, symbol xcex1 represents an angle made by the orthogonal line and the flange-direction line. Then, under the condition given as 0xc2x0 less than xcex1 less than 90xc2x0, the wall surface 214 will interfere with the flange 211, and deforms the flange 211. Under the condition of xcex1xe2x89xa60xc2x0 (xcex1 includes a negative angle), the wall surface 214 will not interfere with the flange 211, and therefore will not deform the flange 211.
In order to prevent the deformation of the flange 211 of the work W caused by the retraction of the rotary cam 213, conventionally, two rotary cams are disposed as show in FIG. 12. Specifically, an end rotary cam 201 is disposed on an axis parallel to the flange-direction line of the flange formed at the end portion of the work, and a main rotary cam 202 for forming the other portion are disposed.
With this arrangement, the end rotary cam 2 has its own axis of rotation L1, whereas the main rotary cam 202 has its own axis of rotation L2, and the two axes are not on a single line. Because the two axes are not on a same line, the negative-angle forming die has to be large, has to have a complex structure, and is expensive. Further, since the end rotary cam 201 and the main rotary cam 202 are not on a single axis but on two separate axes, accuracy is not necessarily sufficient, and it is sometimes impossible to provide a high quality product.
In consideration of the circumstances described above, the present invention aims to dispose the end rotary cam and the main rotary cam on a same axis, thereby simplifying the negative-angle forming die as much as possible and reducing price, and at the same time aims to improve accuracy, thereby making possible to provide a high quality product. According to the present invention, there is provided a rotary cam moving apparatus for a negative-angle forming die comprising a lower die half having a supporting portion for placing a sheet metal work, and an upper die half to be lowered straightly downward onto the lower die half for forming the work, an intrusion forming portion formed in the lower die half at an edge portion near the supporting portion inward of a downward stroke line of the upper die half, a rotary cam rotatably provided in the lower die half, a slide cam including an intrusion forming portion and slidably opposed to the rotary cam, and an automatic retractor provided in the lower die half for pivoting the rotary cam back to a position thereby allowing the work to be taken out of the lower die half after a forming operation, the work placed on the supporting portion of the lower die half being formed by the intrusion forming portion of the rotary cam and the intrusion forming portion of the slide cam, the slide cam forming the work by sliding, the automatic retractor pivoting back the rotary cam after the forming operation for allowing the work to be taken out of the lower die half, wherein a flange is formed at an end portion of the work in a direction across an axis of the pivoting, the work then undergoing an intrusion formation, the flange at the end portion of the work being protected from damage caused by retraction of the rotary cam, by dividing the rotary cam into an end rotary cam for placing the flange formed at the end portion of the work and the main rotary cam for the other portion, both of the divided rotary cams being disposed on a same axis of pivoting, the end rotary cam not being pivoted for an initial predetermined period of the retraction, thereafter the end rotary cam being moved axially toward the main rotary cam.
Further, the present invention provides, specifically, a rotary cam moving apparatus for a negative-angle forming die, wherein for holding the end rotary cam unmoved for an initial period of the retraction, the end rotary cam is formed with a slant end face facing the main rotary cam, the main rotary cam having an end face including half of the face formed as a slant face for contact with the above slant face and the other half of the face formed as an orthogonal face, a transmission pin being provided on the end face of the main rotary cam facing the end rotary cam, at a place radially spaced from the axis of rotation, the slant surface of the end rotary cam being formed with a long arcuate groove for accepting the transmission pin, an urging member for keeping the end rotary cam in an attitude of the intrusion formation being provided between the end rotary cam and the lower die half, and for moving the end rotary cam toward the main rotary cam after the predetermined amount of pivoting of the main rotary cam, a cam follower being provided at an end portion of the end rotary cam, and the lower die half being formed with a cam groove for guiding the cam follower.